scholarly journals On the evolution of the Snow Line in Protoplanetary Discs

2013 ◽  
Vol 8 (S299) ◽  
pp. 167-168
Author(s):  
Rebecca G. Martin ◽  
Mario Livio
Keyword(s):  
Steady State ◽  
Accretion Rate ◽  
Dead Zone ◽  
Giant Planets ◽  
Rotational Instability ◽  
Sufficient Time ◽  
The Earth ◽  
Snow Line ◽  
The Dead ◽  
Protoplanetary Discs

AbstractWe examine the evolution of the snow line in a protoplanetary disc. If the magneto-rotational instability (MRI) drives turbulence throughout the disc, there is a unique snow line outside of which the disc is icy. The snow line moves closer to the star as the infall accretion rate drops. Because the snow line moves inside the radius of the Earth's orbit, the formation of our water-devoid planet is difficult with this model. However, protoplanetary discs are not likely to be sufficiently ionised to be fully turbulent. A dead zone at the mid-plane slows the flow of material through the disc and a global steady state cannot be achieved. We model the evolution of the snow line also in a disc with a dead zone. As the mass is accumulating, the outer parts of the dead zone become self gravitating, heat the massive disc and thus the outer snow line does not come inside the radius of the Earth's orbit. With this model there is sufficient time and mass in the disc for the Earth to form from water-devoid planetesimals at a radius of 1AU. Furthermore, the additional inner icy region within the dead zone predicted by this model may allow for the formation of giant planets close to their host star without the need for much migration.

MRI-accreting inner regions of protoplanetary discs

2021 ◽  
Author(s):  
Marija Jankovic ◽  
Subhanjoy Mohanty ◽  
James Owen ◽  
Jonathan Tan
Keyword(s):  
Steady State ◽  
Energy Transport ◽  
Accretion Rate ◽  
Accretion Disc ◽  
Rotational Instability ◽  
Short Period ◽  
Dust Effects ◽  
Thermal Sources ◽  
Gas Ratio ◽  
Protoplanetary Discs

<p>Short-period super-Earths and mini-Neptunes have been shown to be common, yet it is still not understood how and where inside protoplanetary discs they could have formed. To form these planets at the short periods at which they are detected, the inner regions of protoplanetary discs must be enriched in dust. Dust could accumulate in the inner disc if the innermost regions accrete via the magneto-rotational instability (MRI). We developed a model of the inner disc which includes MRI-driven accretion, disc heating by both accretion and stellar irradiation, vertical energy transport, dust opacities, dust effects on disc ionization, thermal and non-thermal sources of ionization. The inner disc is assumed to be in steady state, and the dust is assumed to be well-mixed with the gas. Using this model, we explore how various disc and stellar parameters affect the structure of the inner disc and the possibility of dust accumulation. We show that properties of dust strongly affect the size of the MRI-accreting region and whether this region exists at all. Increasing the dust-to-gas ratio increases the size of this region, suggesting that dust may accumulate in the inner disc without suppressing the MRI. Overall, conditions in the inner disc may be more favourable to planet formation earlier in the disc lifetime, while the disc accretion rate is higher.</p>

scholarly journals Zombie vortex instability in the protoplanetary disk: can we find it in the lab?

2019 ◽  
Vol 82 ◽  
pp. 435-444
Author(s):  
G. Facchini ◽  
M. Wang ◽  
P. Marcus ◽  
M. Le Bars
Keyword(s):  
Laboratory Experiments ◽  
Hydrodynamic Instability ◽  
Dead Zone ◽  
Protoplanetary Disk ◽  
Finite Amplitude ◽  
Rotational Instability ◽  
Horizontal Shear ◽  
Viscous Effects ◽  
Vortex Instability ◽  
The Dead

Without instabilities, the gas in the protoplanetary disk approximately a forming protostar remains in orbit rather than falling onto the protostar and completing its formation into a star. Moreover without instabilities in the fluid flow of the gas, the dust grains within the disk’s gas cannot accumulate, agglomerate, and form planets. Keplerian disks are linearly stable by Rayleigh theorem because the angular momentum of the disk increases with increasing radius. This has led to the belief that there exists a large region in protoplanetary disks, known as the dead zone, which is stable to pure hydrodynamic disturbances. The dead zone is also believed to be stable against magneto-rotational instability (MRI) because the disks’ cool temperatures inhibit ionization and therefore prevent the MRI. A recent study Marcus et al. (2013) shows the existence of a new hydrodynamic instability called the Zombie Vortex Instability (ZVI), where successive generations of self-replicating vortices (zombie vortices) fill the disk with turbulence and destabilize it. The instability is triggered by finite-amplitude perturbations, including weak Kolmogorov noise, in stratified flows with Brunt-Väisälä frequency N, background rotation Ω and horizontal shear σ. So far there is no observational evidence of the Zombie Vortex Instability and there are very few laboratory experiments of stratified plane Couette flow with background rotation in the literature. We perform systematic simulations to determine where the Zombie Vortex Instability exists in terms of the control parameters (Reynolds number Re, σ/f and N/f). We present a parameter map showing two regimes where ZVI occurs, and interpret the physics that determines the boundaries of the two regimes. We also discuss the effects of viscosity and the existence of a threshold for Re. Our study on viscous effects, parameter map and its underlying! physics provide guidance for designing practical laboratory experiments in which ZVI could be observed.

scholarly journals Influence of planetary gas accretion on the shape and depth of gaps in protoplanetary discs

2020 ◽  
Vol 643 ◽  
pp. A133 ◽  
Author(s):  
C. Bergez-Casalou ◽  
B. Bitsch ◽  
A. Pierens ◽  
A. Crida ◽  
S. N. Raymond
Keyword(s):  
Accretion Rate ◽  
High Viscosity ◽  
Giant Planets ◽  
Low Viscosity ◽  
Aspect Ratios ◽  
Accretion Rates ◽  
Gap Opening ◽  
Hydrodynamical Simulations ◽  
Gas Accretion ◽  
Protoplanetary Discs

It is widely known that giant planets have the capacity to open deep gaps in their natal gaseous protoplanetary discs. It is unclear, however, how gas accretion onto growing planets influences the shape and depth of their growing gaps. We performed isothermal hydrodynamical simulations with the Fargo-2D1D code, which assumes planets accreting gas within full discs that range from 0.1 to 260 AU. The gas accretion routine uses a sink cell approach, in which different accretion rates are used to cope with the broad range of gas accretion rates cited in the literature. We find that the planetary gas accretion rate increases for larger disc aspect ratios and greater viscosities. Our main results show that gas accretion has an important impact on the gap-opening mass: we find that when the disc responds slowly to a change in planetary mass (i.e., at low viscosity), the gap-opening mass scales with the planetary accretion rate, with a higher gas accretion rate resulting in a larger gap-opening mass. On the other hand, if the disc response time is short (i.e., at high viscosity), then gas accretion helps the planet carve a deep gap. As a consequence, higher planetary gas accretion rates result in smaller gap-opening masses. Our results have important implications for the derivation of planet masses from disc observations: depending on the planetary gas accretion rate, the derived masses from ALMA observations might be off by up to a factor of two. We discuss the consequences of the change in the gap-opening mass on the evolution of planetary systems based on the example of the grand tack scenario. Planetary gas accretion also impacts stellar gas accretion, where the influence is minimal due to the presence of a gas-accreting planet.

Pèlerinages barrésiens

2013 ◽  
pp. 116-123
Author(s):  
Claire Bompaire-Evesque
Keyword(s):  
Large Scale ◽  
The Self ◽  
Joan Of Arc ◽  
The Third ◽  
National Importance ◽  
The Earth ◽  
Third Stage ◽  
The Dead

This article is a inquiry about how Barrès (1862-1923) handles the religious rite of pilgrimage. Barrès stages in his writings three successive forms of pilgrimage, revealing what is sacred to him at different times. The pilgrimage to a museum or to the birthplace of an artist is typical for the egotism and the humanism of the young Barrès, expressed in the Cult of the Self (1888-1891). After his conversion to nationalism, Barrès tries to unite the sons of France and to instill in them a solemn reverence for “the earth and the dead” ; for that purpose he encourages in French Amities (1903) pilgrimages to historical places of national importance (battlefields; birthplace of Joan of Arc), building what Nora later called the Realms of Memory. The third stage of Barrès’ intellectual evolution is exemplified by The Sacred Hill (1913). In this book the writer celebrates the places where “the Spirit blows”, and proves open to a large scale of spiritual forces, reaching back to paganism and forward to integrative syncretism, which aims at unifying “the entire realm of the sacred”.

scholarly journals Forming terrestrial planets and delivering water

2015 ◽  
Vol 11 (A29B) ◽  
pp. 427-430
Author(s):  
Kevin J. Walsh
Keyword(s):  
Planet Formation ◽  
Semimajor Axis ◽  
Giant Planet ◽  
Terrestrial Planet ◽  
Giant Planets ◽  
Asteroid Belt ◽  
Terrestrial Planets ◽  
The Earth ◽  
Building Models ◽  
Rich Material

AbstractBuilding models capable of successfully matching the Terrestrial Planet's basic orbital and physical properties has proven difficult. Meanwhile, improved estimates of the nature of water-rich material accreted by the Earth, along with the timing of its delivery, have added even more constraints for models to match. While the outer Asteroid Belt seemingly provides a source for water-rich planetesimals, models that delivered enough of them to the still-forming Terrestrial Planets typically failed on other basic constraints - such as the mass of Mars.Recent models of Terrestrial Planet Formation have explored how the gas-driven migration of the Giant Planets can solve long-standing issues with the Earth/Mars size ratio. This model is forced to reproduce the orbital and taxonomic distribution of bodies in the Asteroid Belt from a much wider range of semimajor axis than previously considered. In doing so, it also provides a mechanism to feed planetesimals from between and beyond the Giant Planet formation region to the still-forming Terrestrial Planets.

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